1. Field of the Invention
The present invention relates generally to eyeglass lenses and more particularly to preparation of multifocal lenses for eyeglass frames.
2. Related Art
Multifocal lenses for eyeglasses, such as bifocal or trifocal lenses, have a primary lens and at least one auxiliary lens segment having a different focal length than the primary lens. Generally, the auxiliary lens is integrated into the primary lens and located near the bottom of the primary lens. Properly locating the auxiliary lens on the primary lens can be difficult due to differences in the geometry of various eyeglass frames and individual patient anatomy. Moreover, each patient may have personal preferences for the location of the auxiliary lens on the primary lens.
An important factor in determining the location of an auxiliary lens on a primary lens is the segment height of the auxiliary lens. The segment height is the distance from the bottom of the primary lens or eyeglasses frame to the top of the auxiliary lens. Often, the segment height is determined by using a ruler, and measuring the distance from the bottom of the frame or lens to the pupil of the patient. This method is problematic, however, because the optical technician must rely on a best guess as to the most comfortable auxiliary lens location for the patient.
Some attempts have been made to mark an eyeglass lens blank with the patient preferred location for the auxiliary lens. This has been accomplished by marking the lens blank with an indicator, such as a piece of transparent tape, while the patient is wearing the eyeglasses. The glasses are then removed from the patient and the segment height is measured with a ruler. Such methods are inherently inefficient because they have required measuring the segment height after removal of the glasses from the patient. Additionally, the indicators have led to placement errors because they don't accurately simulate the auxiliary lens or are difficult for the patient to see.